FIG. 7 is a general view of a tracked hydraulic excavator. The reference numeral 1 denotes an upper revolving works; 2, an undercarriage; and 3, a working unit. The undercarriage 2 is provided with tracks 4, 5 at the left and right thereof. The left and right tracks 4, 5 are driven by a sprocket 6 which is in turn driven by a hydraulic motor, and thus the vehicle travels. The reference numeral 7 denotes a cab, which faces in a direction depicted by an arrow. Steering is performed by changing a travel speed of the left and right tracks 4, 5 or reversing a traveling direction thereof. The upper revolving works 1 can swing 360.degree. with respect to the undercarriage 2.
FIG. 8 is a side view showing a conventional cab of a hydraulic excavator, FIG. 9 is a plan view of the cab, and FIG. 10 is a front view of the cab. Left and right traveling levers 81, 82 and left and right traveling pedals 83, 84 are disposed ahead of a seat 80. The left traveling lever 81 and the left traveling pedal 83 are secured to each other. The right traveling lever 82 and the right traveling pedal 84 are also secured to each other. The reference numerals 85 and 86 denote left and right foot rests, and 90 and 91 indicate left and right working unit control levers.
As for traveling operations, when the left traveling lever 81 or the left traveling pedal 83 is pivoted forwardly, the left track 4 moves forwardly. Also, pivoting the left traveling lever 81 or the left traveling pedal 83 rearwardly causes the track 4 to move rearwardly. When the right traveling lever 82 or the right traveling pedal 84 is pivoted forwardly or rearwardly, the right track 5 moves forwardly or rearwardly. The traveling speed is proportional to a control input of the traveling levers or the traveling pedals. Operating either one of the traveling levers or one of the traveling pedals causes an on-the-spot turn. While operating the left and right traveling levers 81, 82 or the left and right traveling pedals 83, 84 in the same direction, changing the left and right control inputs causes the vehicle to make a slow turn. Operating the left and right traveling levers 81, 82 or the left and right traveling pedals 83, 84 in opposite directions to each other causes the vehicle to make a quick on-the-spot turn.
According to the above mentioned construction, the left and right traveling levers 81, 82 or the left and right traveling pedals 83, 84, disposed ahead of the seat 80, are operated for traveling the vehicle or for making an on-the-spot or a quick on-the-spot turn. However, this involves the following problems:
(1) The left and right traveling levers 81, 82 obstruct the front visibility.
(2) When an operator sits in or leaves the seat 80, the left and right traveling levers 81, 82 are in the operator's way.
(3) When the operator looks ahead and down for deep excavation, the left and right traveling levers 81, 82 obstruct the view of the excavation work.
(4) When the operator steps on the left and right traveling pedals 83, 84 for operation thereof, the left and right traveling levers 81, 82 abut the operator's feet to interfere with the foot operation.
(5) When the left and right traveling levers 81, 82 oscillate due to vibrations of the body of the vehicle, the vehicle may move. To prevent this, it is necessary to employ a strong spring, damper and the like for maintaining neutrality. However, a poor return due to a spring force or damper causes hindrance to traveling operations with a resultant difficulty in a fine operation.
(6) Since the left and right traveling pedals 83, 84 are in a balance-like structure, the position of a fulcrum is indefinite with a resultant difficulty in a fine operation.
(7) For pivoting the left and right traveling pedals 83, 84 rearwardly, a heel is used to step on them. This operation, however, is hard to perform.
(8) A composite operation requires the concurrent use of both feet.